[POS] Interdisciplinary Studies

[POS-66] Coevolution of cooperation and exit strategies under varied forms of environmental pressure

*Natsuki Ogusu¹, Wataru Toyokawa^1,2,3 (1. Riken (Japan), 2. University of Konstanz (Germany), 3. Max Planck Institute of Animal Behaviour (Germany))

Keywords:

cooperation,behavior ecology,agent-based model,cultural psychology

The option to exit uncooperative partners has been considered a potential mechanism to enhance cooperation in a population under repeated social dilemma games, since individuals should be cooperative to avoid being abandoned by other cooperative partners and hence losing future benefits (Hayashi & Yamagishi, 1998). Theory predicts that the traits of being cooperative and demanding others to be cooperative would coevolve to stabilize a cooperative relationship. On the other hand, empirical studies in cultural psychology have suggested that the mobility of the relationship when the social partners are uncooperative varies across populations, which can shape the concomitant cooperation level (Thomson et al., 2018). Previous research has discussed that harsher environmental conditions require tighter relationships and lead the population to lower the exit thresholds as well as the cooperation level. However, this hypothesis has not yet been examined from a mathematical perspective.To test this hypothesis, we built an agent-based model investigating the conditions under which the evolution of cooperation and exit threshold levels are affected. Within a generation, each agent exhibits genetically fixed behavior of cooperation and exit. The agents played the two-player public goods game with continuous contribution. In some scenarios, we allow them to exit from partners when their contribution is lower than the exit threshold of the focal agent.We found that allowing exit did not always promote cooperation when generation times were short and the initial population contained fewer cooperators, even in the absence of environmental pressures that directly reduce individual payoffs. We also found that environmental harshness itself functioned to maintain cooperation above a certain level when exit was not permitted. Variables that could be interpreted as indicators of environmental harshness, such as shorter generation times, smaller population sizes, higher survival costs per time-step, pressures that can only be mitigated through long-term mutual cooperation, and upper limits on the resource storage, sometimes suppress the levels of cooperation and exit thresholds, though this was not always the case. In some settings, the collapse of cooperation and extinction in easier environments were more likely to occur when we allow exit. We will discuss future directions for testing the theoretical implications, both mathematically and empirically.